1. Field of the Invention
The subject invention generally relates to methods and apparatus for transporting heat-generating loads through environments affected by vibrations and substantial pressure variations and, more particularly, to vibration isolators that act as heat sinks, and to heat pipe systems with vibration damping or isolating functions.
2. Information Disclosure Statement
The following disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments which may be subsequent in time or priority.
Also, no preamble of any statement of invention or claim hereof is intended to represent that the content of that preamble is prior art, particularly where one or more recitations in a preamble serve the purpose of providing antecedents for the remainder of a statement of invention or claim.
In his article, "THE HEAT PIPE," G. Yale Eastman (SCIENTIFIC AMERICAN, vol. 218, May 1968), points out that even copper and other metals are poor conductors of heat, giving a numerical example for that fact. He then relates how the principle of the heat pipe was first put forward in 1942 by Richard S. Gaugler of the General Motors Corporation, and was rediscovered in 1963 by George M. Grover of the Los Alamos Scientific Laboratory.
In the meantime, with the advent of the transistor, ways and means were sought for cooling electronic equipment by establishing a liquid vaporization and recondensation cycle thereat, as may, for instance, be seen from U.S. Pat. No. 2,958,021, by B. Cornelison et al, issued Oct. 25, 1960, for Cooling Arrangement for Transistor. That proposal lacked the capillary element necessary for the heat pipe cycle. A subsequent proposal provided such a capillary element in the form of a flexible wick, as may be seen from U.S. Pat. No. 3,957,107, by F. Altoz et al, issued May 18, 1976, for a Thermal Switch.
In particular, that Altoz et al U.S. Pat. No. 3,957,107 teaches the use of conventional heat-insulating standoff support members for mounting what they call a "hot plate" on top of a "cold plate." The equipment that is temperature controlled is thermally attached to the hot plate. The cold plate may be the skin of an aircraft, the wall of a heat exchanger, or another heat sink. The heat pipe structure is located between the cold and hot plates, having a bottom plate attached to the cold plate and including an expansible bellows extending from that bottom plate and mounting a top plate in spaced relationship to the hot plate. The above mentioned capillary wick extends between these bottom and top plates inside the bellows, wherein the working fluid is contained.
In the thermal switch of that Altoz et al U.S. Pat. No. 3,957,107, the thermal impedence along the heat pipe and from the hot plate to the cold plate is very high. In fact, that heat pipe structure can only become operative if the cold plate becomes overheated. In that case, such excessive heat energy enters the heat pipe structure through its bottom plate until the working liquid starts to evaporate and expand the encompassing bellows. This moves the spaced top plate of the heat pipe structure toward and eventually into contact with the hot plate, whereby that thermal switch in effect closes to conduct heat away from the hot plate through the now expanded heat pipe structure to the cold plate. After the emergency condition has ceased, the heat pipe structure switches to its normal high impedence state.
Another kind of switching in a heat pipe system is disclosed in U.S. Pat. No. 4,000,776, by H. L. Kroebig et al, issued Jan. 4, 1977. In that case, the heat pipe wick is normally held in contact with a heat sink, for removing heat from a component inside a structure to the outside thereof. In order to prevent reverse flow of heat, the heat pipe structure is provided with a bellows that contains an expansible fluid. When the outside of the structure heats up, the bellows moves the wick away from the heat sink, thereby effectively eliminating the evaporator for the reverse heat flow system. That patent thus provided a heat pipe system which effectively acted as a heat pipe diode.
U.S. Pat. No. 4,118,756, by L. A. Nelson et al, issued Oct. 3, 1978, proposes a heat pipe thermal mounting plate including a thick artery wick and thin condenser and evaporator wicks for cooling electronic circuit cards.
U.S. Pat. No. 4,212,349, by F. E. Andros et al, issued July 15, 1980 for a Micro Bellows Thermo Capsule. In an effort to eliminate the need for a capillary wick, that patent proposes formation of an internal vapor bubble through which vapor is to flow to a condenser section, and along which condensate is to return to an opposite evaporator section. That vapor bubble arrangement is preferably disposed in a micro bellows capsule to enable absorption of stresses in the system during operation and to provide a metallurgical bond independently of the tolerances of the total system.
A similar arrangement has been disclosed in U.S. Pat. No. 4,313,492, by F. E. Andros et al, issued Feb. 2, 1982 for a Micro Helix Thermo Capsule. According to that patent, a quantity of coolant liquid is disposed in a container comprising a flexible cylindrical bellows having a helical convolution providing a capillary passage between spaced condenser and evaporator sections.
Reference may also be had to U.S. Pat. No. 4,402,358, by D. A. Wolf, issued Sept. 6, 1983, for a Heat Pipe Thermal Switch. That thermal switch includes a flexible bellows defining an expansible vapor chamber for a working fluid located between evaporation and condensation chambers. A coiled retaining spring and several axial wicks are located inside that bellows. The evaporation and condensation chambers are connected by turnbuckles and tension springs to provide a set point adjustment for setting the gap between an interface plate on the condensation chamber and a heat sink for the thermal switching action contemplated by that reference.
Of course, as in the above mentioned Altoz et al U.S. Pat. No. 3,957,107, standoff support members have to be provided between the "hot" and "cold" plates, so as to provide for the initial gap between the interface plate of the thermal switch and the heat sink, which enables the switching action desired in those references, but which transmits vibrations along the standoff members to the load.
None of these references protects the heat transfer cycle in the heat pipe against pressure variations occurring externally of its enclosure. In practice, this may impair the applicability of prior-art proposals to airborne or other systems exposed to pressure variations occurring externally of the heat pipe structure.